Airbag with flame retardant monolithic coating layer

ABSTRACT

Provided herein are specific coating compositions, which are used as a monolithic coating layer for airbags. Preferably, these coating compositions are comprised of urethanes, which are blended together, where at least one of the urethane components is inherently flame retardant and the other of which is a urethane with gas-retaining properties. The gas-retaining urethane may be characterized as having high tensile strength at break, high elongation at break, and a 100% modulus less than 2,000 p.s.i. The inherently flame retardant urethane is the result of a manufacturing process in which a halogenated diol is reacted with an isocyanate, resulting in the incorporation of halogens into the polyurethane backbone. The resulting coating compositions (that is, the blends of gas-retaining urethane and flame retardant urethane), when applied as a single layer to an airbag fabric, result in an airbag with good gas retention, flame retardance, anti-blocking properties, and aging stability.

TECHNICAL FIELD

The present disclosure relates to the use of a monolithic,flame-retardant coating for airbag fabrics. The flame retardant coatingcomposition imparts desired properties to the airbag, such as gasretention, flame retardance, anti-blocking, and aging stability, whichhave heretofore been achievable only with multiple coating layers. Thecoating composition comprises a blend of at least two differenturethanes, one of which is inherently flame retardant urethane and theother of which is a gas-retaining urethane compound. The primaryadvantage of the present coating composition is that, even when used asa single layer, it achieves the desired properties of a two-layercoating system.

BACKGROUND

Historically, airbags have been coated with one or more layers ofpolymeric material to enhance their performance, for example, bypreventing the unwanted permeation of air through the fabric and, to alesser extent, by protecting the fabric from detriment due to exposureto hot gases used to inflate the airbags. Polychloroprene was thepolymer of choice in the early development of coated airbags. However,it was subsequently discovered that, when exposed to heat,polychloroprene tends to degrade and to release the components ofhydrochloric acid, thereby potentially introducing hazardous chemicalsinto the surrounding and degrading the fabric component. Thisdegradation issue, coupled with the desire to decrease the folded sizeof the completed airbag by using less coating material, led to thealmost universal replacement of polychloroprene with silicone-basedmaterials for use as airbag coatings.

Newer designs for airbags, particularly those being placed in the sidesof passenger compartments, have introduced the requirement that the bagshold pressure longer under use. The requirement of longer air retentiontimes and the use of lower coating levels of silicone polymer havehighlighted the effect that a naturally lubricating silicone coatingwill allow the yarns in the airbag fabric to shift when a sewn seam isstressed. This shifting may lead to leakage of the inflating gas throughpores formed from the shifting yarns or, in drastic cases, may cause theseam to fail. Since the airbag must retain its integrity during acollision event in order to sufficiently protect the vehicle occupants,there is a great need to provide coatings that provide both effectiveair retention characteristics and sufficient restriction of yarnshifting for the airbag to function properly.

As mentioned above, in recent years, silicone coatings have beenutilized to provide such desired permeability and strengthcharacteristics. Most often, these properties have been achieved byapplying a first layer of gas-retaining polymer (such as asilicone-containing polymer) to the fabric surface and by applying asecond, protective layer over the first layer. The second, protectivelayer prevents the airbag coating from sticking to itself when foldedand stored (a condition known as “blocking”) and also protects thefirst, gas-retaining layer from damage due to aging, abrasion, and thelike. In most situations, the second layer also helps to minimize theburn rate of the airbag to achieve a passing score on the horizontalburn test mandated by Federal Motor Vehicle Safety Standard (FMVSS) 302.

Often, polymers including polyurethane, acrylics, and the like are used,either as components of a silicone layer (as in the case of blends,hybrids, or interpenetrating polymer networks) or as separate coatinglayers, perhaps with a silicone-containing layer. Efforts to createmulti-component airbag coatings have previously focused on combiningsilicone with different polymers in the same polymer network. U.S. Pat.Nos. 6,348,543; 6,468,929; and 6,545,092, all to Parker, describe theproduction of an airbag coating made of a vinyl-containing polysiloxanecross-linked to, or admixed with, an ethylene-containing copolymer, suchas ethylene methyl acrylate or ethylene vinyl acetate. In an alternateapproach, described in U.S. Pat. No. 6,846,004 to Parker, a siliconepolymer is combined with a copolymer of ethylene and at least one polarmonomer in the presence of a volatile solvent and, optionally, a curingcatalyst. Yet another approach, which is described in US PatentApplication Publication No. 2005-0100692 to Parker, involves coating theairbag fabrics with the cross-linked reaction product of avinyl-containing silicone and a copolymer having silicone andnon-silicone substituents, which may or may not have terminal Si—Hgroups.

In the area of multiple-layered coating systems, U.S. Pat. Nos.6,239,046 and 6,641,686, both to Veiga et al., describe the use of atwo-layer airbag coating, where the fabric-contacting layer is anadhesive polyurethane and the top layer is an elastomeric polysiloxane.Another approach, described in U.S. Pat. No. 6,734,123 to Veiga et al.,uses multiple layers of polyurethane as the airbag coating material. Inthis instance, layers of adhesive polyurethane and elastomericpolyurethane are employed to achieve the desired properties. Yet anothermulti-layer coating system is provided in U.S. Pat. No. 6,770,578 toVeiga, in which a prime coat of polyurethane is applied to an airbagfabric, followed by one or more layers of polymer film. Such polymerfilms are formed of polyurethane, polyamide, or polyolefin.

U.S. Pat. No. 6,177,365 and U.S. Pat. No. 6,177,366, both to Li,describe airbag coating compositions comprising at least two separateand distinct layers. The first layer (base coat), being in contact withthe airbag surface, comprises a non-silicone composition of at least onecoating material and provides excellent adhesion, excellent tensilestrength, and lower cost than standard silicone materials. The secondlayer, being a coating for the first layer, provides excellentreinforcement and aging characteristics to prevent degradation of thefirst layer. Such a second layer (topcoat) is preferably a siliconematerial. This two-layer system permits excellent strength and agingproperties to prevent seam combing at relatively low cost due to theinexpensive basecoat materials and the relatively low add-on weightrequired for the topcoat.

Airbag manufacturers have used these and other solutions to address themultiple problems associated with forming a suitable coatingcomposition. Most importantly, the airbag coating needs to provide thenecessary gas-retention properties to the airbag. Secondly, the coatingneeds to impart flame retardance to the airbag. Historically, thisproblem has been solved by incorporating flame retardant additives intothe top layer(s) of the coating, since the incorporation of flameretardant additives into the fabric-contacting layer impairs gasretention. A third problem faced by manufacturers is that the coatingcompositions tend to stick to themselves, when the bags are folded andstored over long periods. This issue, known as “blocking”, may cause theairbag coating to adhere to itself and pull away from the airbag as itis deployed. Finally, yet another problem is the need for the airbagcoating to be stable to aging, meaning that the coating will not degradeover time and in extreme conditions of heat and/or humidity.

To date, no airbag manufacturers have been able to solve these problemswith a single coating layer, which would be advantageous in terms of rawmaterial and manufacturing costs. The present urethane-based coatingcomposition, which may be used as a monolithic coating layer forairbags, provides a solution to these issues.

SUMMARY

Provided herein are specific coating compositions, which are used as amonolithic coating layer for airbags. Preferably, these coatingcompositions are comprised of urethanes, which are blended together,where at least one of the urethane components is inherently flameretardant and the other of which is a urethane with gas-retainingproperties. The gas-retaining urethane may be characterized as havinghigh tensile strength at break, high elongation at break, and a 100%modulus less than 2,000 p.s.i. The inherently flame retardant urethaneis the result of a manufacturing process in which a halogenated diol isreacted with an isocyanate, resulting in the incorporation of halogensinto the polyurethane backbone. The resulting coating compositions (thatis, the blends of gas-retaining urethane and flame retardant urethane),when applied as a single layer to an airbag fabric, result in an airbagwith good gas retention, flame retardance, anti-blocking properties, andaging stability.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph showing the leak-down rates over time of airbagscoated with the present coating composition as first produced and aftertwo different aging tests.

DETAILED DESCRIPTION Urethane Production

Two different urethanes are blended together, preferably in an aqueousdispersion, to produce the present coating composition.

The first urethane is engineered to produce excellent gas-retainingproperties and, as such, will be referred to herein as the“gas-retaining urethane.” The gas-retaining urethane is characterized ashaving high tensile strength at break (for instance, at least 2,500p.s.i.), high elongation at break (for instance, at least 300%), and a100% modulus less than 2,000 p.s.i. Typically, polycarbonate-basedpolyurethanes provide better gas retention properties than polyether- orpolyester-based polyurethanes. In addition, polycarbonate-basedpolyurethanes tend to have the fewest degradation issues under normalairbag environmental (i.e., heat and humidity) aging conditions. It isalso possible to use hybrids (that is, polyurethanes having bothpolycarbonate and polyether diols) for the gas-retaining urethanecomponent.

The second urethane is an inherently flame retardant urethane and willbe referred to herein as the “flame retardant urethane.” The inherentlyflame retardant urethane is the result of a manufacturing process inwhich a halogenated diol is used as one of the starting materials, alongwith a polyol and an isocyanate. Advantageously, the inclusion of ahalogenated compound (especially a brominated compound) in the urethanebackbone eliminates the need for subsequently added flame retardantadditives, which are often more difficult to incorporate into a coatingcomposition. Preferably, the halogenated compound is a brominatedpolyol. Preferably, the brominated polyol is present in an amount offrom about 10% to about 50% of the polyols used in making the flameretardant polyurethane. The flame retardant urethane is characterized ashaving a tensile strength greater than about 1,200 p.s.i.; morepreferably, in the range of about 2,000 p.s.i. to about 2,500 p.s.i.;and, most preferably, greater than about 2,500 p.s.i.

The ratio of gas-retaining polyurethane to flame retardant polyurethaneis preferably around between 80/20 and 50/50, by weight. In oneembodiment, the ratio of gas-retaining polyurethane to flame retardantpolyurethane is 70/30. In another, potentially preferred embodiment, theratio of gas-retaining polyurethane to flame retardant polyurethane is60/40. These ratios—each of which includes at least 50% of thegas-retaining polyurethane—ensure that the coating formulations exhibita good balance of gas retention and flammability characteristics.

To produce the desired polyurethanes mentioned above, it is necessary toselect the appropriate starting materials (one or more polyols,isocyanate, and chain extenders), molar ratios (especially the ratio ofpolyol to isocyanate), and reaction conditions. The molar ratio ofpolyol compound(s) to isocyanate compound is preferably on the order of0.5:1 to 0.98:1.

Preferred polyols for producing a polyurethane include polycarbonatepolyols, polyether polyols, silicon-based diols, olefin-based diols,polyester diols, and combinations thereof, the structures thereof beingshown below as (I) through (VI). A single polyol may be used for thegas-retaining polyurethane, although two or more polyols may instead beused. By way of example only, and without limitation, blends ofpolycarbonate polyol and polyether polyol (e.g., in ratios of from about80/20 to about 50/50, respectively) may be used to produce agas-retaining polyurethane compound.

Polycarbonate polyols include compounds having a structure according tostructures (I) and (II) below:

where R and R₁ are selected from the group consisting of aliphaticradicals and aromatic radicals, where R₂ is selected from the groupconsisting of aliphatic hydrocarbon groups having between 4 to 10 carbonatoms and alicyclic hydrocarbon groups having between 4 to 10 carbonatoms, and n is an integer between 2 and 20. In one embodiment, R is(CH₂)₆, resulting in a polycarbonate polyol with an average molecularweight (Me) of about 2,000.

Exemplary polyether polyols include compounds having a structureaccording to structure (III) below:

where n is an integer between 5 and 68. One representative polyetherglycol is polypropylene glycol, having a molecular weight (M_(n))between 400 and 4,000. Also included in this class of polyols areolefin-based diols, which include compounds having a polyethylene, apolypropylene, or a polyolefin copolymer, where the copolymer has ahydroxyl group in a terminal and/or side chain position.

Exemplary silicon-based diols include compounds having a chemicalstructure according to structure (IV) below:

HO—R₁—[—OSiR₂R₃—]—R₄—OH  (IV)

where R₁ and R₄ are independently selected from the group consisting ofaromatic and aliphatic radicals and where R₂ and R₃ are independentlyselected from the group consisting of methyl radicals, hydroxylradicals, phenyl radicals, and hydrogen.

Exemplary polyester-based diols include the two compounds whose chemicalstructures (V) and (VI) are shown below:

where R is selected from the group consisting of aliphatic hydrocarbongroups having between 2 and 10 carbon atoms and alicyclic hydrocarbongroups having between 2 and 10 carbon groups and where n is an integerchosen to provide a M_(n) for the polyol of between about 1,000 andabout 2,400.

Due to their color stability and heat stability, aliphatic isocyanatesare preferred for reaction with the polyols described above. Suitablealiphatic isocyanates include, but are not limited to, 1,6-hexamethylenediisocyanate (HDI), isophorane diisocyanate (IPDI), hydrogenatedmethylenediphenyl diisocyanate (HMDI), andα,α,α′,α′-tetramethyl-m-xylene diisocyanate (m-TMXDI).

In some circumstances, it may be desirable to use a catalyst to promotethe reaction between the polymer diol and the isocyanate compound.Suitable catalysts include tertiary amines, organic tin compounds, andother catalysts known for this purpose.

Typically, water-based polyurethane dispersions are produced using atwo-stage synthesis. The first stage involves the manufacture of amoderately low molecular weight, hydrophobic polyurethane oligomerhaving terminal isocyanate groups. This moderately low molecular weightoligomer is the reaction product of a multifunctional (usuallydifunctional) isocyanate with polyhydroxy compounds to produce an NH—COOurethane linkage. Such a reaction is shown below, where the polyol andthe isocyanate are represented with generic structures. For water-basedsyntheses, at least one of the polyhydroxy compounds is ionic in nature,typically a dihydroxy organic acid, such as dimethylolpropionic acid(DMPA).

A representative reaction is shown below.

A wide variety of polyhydroxy compounds available for this synthesisreaction leads to the versatility of the polyurethane polymer. Forexample, in the production of an inherently flame retardantpolyurethane, one of the polyhydroxy compounds is a halogenatedpolyhydroxy.

Due to the selective reactivity of the polyisocyanate, the acidfunctionality of the dihydroxy organic acid compound is extremelyslow-reacting, as compared to primary or even secondary hydroxyl groups.This reactivity difference allows the reaction of the hydroxyl groupsfrom the polyols—including the hydroxyl groups from dihydroxy organicacid—with excess polyisocyanate to yield the isocyanate-terminatedpolyurethane oligomer, shown above, which has a determinable amount ofionic functionality built within the oligomer backbone. As shown above,the ionic functionality is due to the presence of carboxylic acidgroups. It should also be understood that compounds having sulfuric acidgroups (SO₃H), in place of the carboxylic acid groups, may instead beused.

By combining one of a large array of polyhydroxy compounds and one ofseveral choices of polyisocyanate compounds, there is the ability totailor design performance characteristics to meet specific, requiredparameters, which may range from extremely low modulus with surface tackto low modulus with high tensile strength and elongation to high moduluswith high tensile to extremely low elongation and brittleness. In thecase of airbag coatings, it is desirable to provide a coating withrelatively high tensile strength, high elongation, and low tack.

The isocyanate-terminated polyurethane oligomer, shown above, istypically quite viscous. As a result, a dispersion solvent is needed todilute the oligomer. Most often, N-methylpyrrolidone (NMP) is used forthis purpose.

The second stage of the production of the desired polyurethane compoundsinvolves complexing the ionic functionality, which is present in thehydrophobic (oil-based) oligomer, to create a water-dispersible(hydrophilic) urethane prepolymer. The hydrophilic urethane prepolymermay then be dispersed, under medium shear conditions. Typically, suchcomplexing is achieved by introduction of a base, such as a volatiletertiary amine (represented as NEt₃ in the reaction shown below).

Stahl USA, Inc. of Peabody, Mass.; Bayer MaterialScience, LLC ofPittsburgh, Pa.; and Hauthaway Corporation of Lynn, Mass. manufactureone or more commercially available gas-retaining urethanes, which aresuitable for use in the present coating formulations. Additionally,Stahl USA, Inc. and Hauthaway Corporation also manufacture commerciallyavailable flame retardant urethanes, including, but not limited to, analiphatic polycarbonate polyurethane that includes brominated polyolsincorporated therein.

Additives

Once dispersed, the hydrophilic urethane prepolymers (shown above as thereaction product) are extended with a multifunctional amine compound,which quickly reacts with the terminal isocyanate groups to createpolyurea linkages and to promote chain growth. In this manner, themolecular weight of the polyurethane resin is further increased.Multifunctional amine compounds include any organic molecule having atleast two primary amine groups, such as ethylenediamine,hexamethylenediamine, hydrazine, and the like. Again, there issignificant versatility in the types of amine compounds that may be usedfor this purpose, as the molecular weight of these compounds ranges fromabout 32 (for hydrazine) to over 3,000 (for polyetheramines). The amountof amine compound to be introduced is calculated based on the amount ofisocyanate present in the hydrophobic urethane compound at the time ofdispersion. Most often, the amine compounds are present in an amount offrom about 75% to about 95%, by molar ratio, of the isocyanatecompounds.

The coating compositions described herein are particularly suitable forcoating airbag fabrics and airbags. The coating composition may includeone or more of the following optional additives: thickeners, rheologymodifiers, anti-blocking agents, colorants or pigments, heat or UVstabilizers, antioxidants, cross-linking agents, adhesion promoters,fillers, synergists for flammability, and the like. Preferably, rheologymodifiers and thickeners are added to adjust the viscosity of thecoating formulation to between about 25,000 and about 40,000 centipoiseand, more preferably, to between about 30,000 and about 40,000centipoise.

Some anti-blocking agents contribute both to the anti-blocking andflammability properties of the coating composition. Such compoundscontain a high bromine content and have a synergistic fire retardanteffect when combined with the flame retardant polyurethane.

Synergists

Synergists are compounds that enhance some characteristic of thecomponents of the airbag coating formulations. The desired amount ofsynergist(s) may be incorporated into the urethane during thechain-extension stage, as the urethane is being dispersed, or may bepost-added into the urethane dispersion once the urethane ismanufactured. Some synergists are of the flame retardant variety. Manyof these flame retardant synergists do not exhibit significant flameretardant properties when used alone. However, when used with flameretardant urethanes, these synergists increase the overall effectivenessof the flame retardant coating composition, even when present in amountsas small as from about 5% to about 10% by weight of the coatingcomposition.

In flame retardant coating formulations, the use of metal oxides assynergists in organohalogen systems is quite common. Of these, threeoxides have been found to be especially useful. These are antimonytrioxide (ATO), antimony pentoxide (APO), and sodium antimonite.

Application to Airbag Fabrics

As described herein, each of the two polyurethane compounds issynthesized according to the reactions shown above; converted into itshydrophilic prepolymer; dispersed in water with surfactants, defoamers,and other agents, as necessary or desired; and extended to the desiredmolecular weight. The two separate dispersions (that is, thegas-retaining polyurethane dispersion and the flame retardantpolyurethane dispersion) are then combined, via shear mixing, to createa blended coating composition. The appropriate ratios of gas-retainingto flame retardant polyurethane and the appropriate amounts of optionaladditives are described above.

The coating composition, comprising the two urethane components andadditives, is then applied to an airbag fabric by any known coatingmethods, including floating knife coating, knife-over-roll coating,spray coating, impregnation coating, curtain coating, reverse rollcoating, transfer roll coating, and screen coating. The coating is thendried at a temperature in the range from about 260° F. to about 320° F.(from about 127° C. to about 160° C.) and, more preferably, at atemperature of about 300° F. (about 149° C.) for about two minutes. Theadd-on weight of the coating composition, when dry, is preferably fromabout 0.5 oz/yd² to about 1.5 oz/yd²; more preferably, is less thanabout 1.0 oz/yd² (or 34 g/m²); and, in some embodiments, may be lessthan about 0.6 oz/yd² (or 20 g/m²).

Because the coating composition is applied as a single, monolithiclayer, manufacturing is significantly simplified. Rather than applying afirst coating layer, drying it, applying a second layer, and drying it,the present compositions require a single application pass and a singledrying pass.

Moreover, in those cases where anti-blocking characteristics areincorporated within the present coating composition, manufacturing maybe further simplified, by eliminating the need for a separateapplication of an anti-blocking agent to the dried airbag coating.Anti-blocking characteristics may be achieved through the properselection of the bulk properties of the flame retardant and gasretaining urethanes. However, the use of the present coatingcompositions in a monolithic layer does not preclude the separateapplication of an anti-blocking agent (such as spray talc), if desired,as such applications are not considered a separate, or second, coatinglayer.

Example 1

An airbag coating composition to be used as a monolithic layer wasprepared using commercially available urethanes in a dry blend ratio of60:40 gas-retaining urethane to flame retardant urethane. The componentsof the coating composition are provided below.

Parts Parts Component % Solids (Dry) (Wet) Gas-retaining urethane 4060.00 150.00 Flame retardant urethane 35 40.00 114.29 Anti-blockingagent 60 5.00 8.33 Rheology modifier 25 2.30 9.20 Pigment 40 0.90 2.25The finished coating composition had a viscosity of approximately 34,000centipoise and was readily spreadable via floating knife coater. Thecoating composition was applied, using a floating knife coater, in asingle layer to both outer sides of a one-piece Jacquard woven sidecurtain-type airbag. The airbag had a 52×50 construction and used 420denier nylon 6,6 yarns in both the warp and fill directions.

The coated bag was then dried in an oven at a temperature of about 300°F. (about 149° C.) for about 2 minutes. The dry add-on weight of thecoating composition (on each side of the airbag) was about 0.5 oz/yd² or17 g/m². No talc or other anti-blocking agents were added to the coatedbag.

Example 2 Comparative

A comparative Example was created in which two different coating layerswere applied sequentially to an airbag fabric. The components of thevarious coating layers are shown below.

Layer 1: Fabric-Contacting Layer Parts Parts Component % Solids (Dry)(Wet) Gas-retaining urethane 40 80.00 200.00 Acrylic polymer 60 20.0033.33 Rheology modifier 15 2.00 13.33 Pigment 40 0.03 0.08The fabric-contacting coating composition was applied, using a floatingknife coater, in a single layer to both outer sides of a one-pieceJacquard woven side curtain-type airbag. The airbag had a 52×50construction and used 420 denier nylon 6,6 yarns in both the warp andfill directions.

The coated fabric was then dried in an oven at a temperature of about300° F. (about 149° C.) for about 2 minutes. The dry add-on weight ofthe first layer (on each side of the airbag) was about 0.5 oz/yd² or 17g/m².

Layer 2: Top-Coat Layer Component % Solids Parts (Dry) SiliconeComponent “Part A” 100 50.00 Silicone Component “Part B” 100 50.00The top-coat layer composition was applied, using a floating knifecoater, over the fabric-contacting layer. The coated fabric was thendried a second time in an oven at a temperature of about 360° F. (about182° C.) for about 1.5 minutes. The dry add-on weight of the secondlayer (on each side of the airbag) was about 1.0 oz/yd² or 34 g/m². Thecoated airbag fabric was then lightly sprayed with talc to preventblocking.

Evaluation of Examples

Examples 1 and 2 were evaluated for a variety of properties, the resultsof such analyses being shown below. Where appropriate, standard testmethods are listed in parentheses following the test descriptions.

Description (Test Method) Units Example 1 Example 2 Weave Count - WarpPer 51.0 52.3 (ISO7211/2 Method C) 25.4 mm Weave Count - Fill Per 50.050.3 (ISO7211/2 Method C) 25.4 mm Total Weight A (ASTM D-3776C) oz/yd²6.5 7.6 Coating Add-on “A” Side g/m² 13.6 51.2 Total Weight B (ASTMD-3776C) oz/yd² 6.5 7.6 Coating Add-on “B” Side g/m² 13.0 49.6 Tensile -Warp (ASTM D-5034) N 2576 2540 Tensile - Fill (ASTM D-5034) N 2716 2654Elongation - Warp (ASTM D-5034) % 45.1 45.8 Elongation - Fill (ASTMD-5034) N 43.9 48.2 Joint Tensile - Warp (ASTM D-1683) N 1542 1474 JointTensile - Fill (ASTM D-1683) N 1403 1466 Tongue Tear Strength - Warp N134 180 (ASTM D-2261) Tongue Tear Strength - Fill N 144 206 (ASTMD-2251) Flammability - Warp (FMVSS 302) Pass/Fail Pass PassFlammability - Fill (FMVSS 302) Pass/Fail Pass Pass Stiffness/CircularBend - Warp N 14.0 11.6 (ASTM D-4032) Stiffness/Circular Bend - Fill N12.7 11.0 (ASTM D-4032)These results indicate that the monolithic coating composition of thepresent disclosure performs equally well as the standard, two-layercoating composition, in terms of flammability and tensile strength.Importantly, the present monolithic coating was able to meetflammability requirements without the necessity of a second (top) coatto provide flame retardance.

As described previously, gas retention is important in protecting avehicle's occupants from injury, especially in the event of a vehiclerollover. Gas retention is measured by inflating an airbag (in thiscase, a side-curtain, one-piece woven airbag) to a peak pressure of 70kPa and then recording the pressure retention as a function of time. Thetime for deflation was measured and has been plotted in FIG. 1. FIG. 1shows the gas retention rates for three airbags of the same construction(materials, size, shape, and volume), which were coated with theformulation of Example 1.

A first airbag was tested immediately after production (as indicated inFIG. 1 by the label “As Received” and with a line comprised ofsquare-shaped points).

A second airbag was subjected to environmental testing by heat-aging thecoated airbag at 105° C. for 14 days (as indicated in FIG. 1 by thelabel “Heat Aged at 105 C/14 Days” and with a line comprised oftriangle-shaped points).

A third airbag was subjected to environmental testing by subjecting thecoated airbag to a temperature of 80° C. and 95% relative humidity for14 days (as indicated in FIG. 1 by the label “80 C/95% RH/14 Days” andwith a line comprised of circular points).

As shown in the FIGURE, the elimination of the second (top) coatinglayer from the airbag coating system had no effect on the airbags coatedwith the present coating system. Even after vigorous environmentaltesting, the gas-retaining properties of the present coating system arenot significantly reduced. The gas-retaining properties remainsubstantially the same (and in an acceptable range) as the “As Received”sample.

Another test used to evaluate Examples 1 and 2 is called a “blockingtest,” which indicates the force required to separate two portions ofcoated fabric from one another after prolonged storage in contact witheach other (such as an airbag is stored). This test was conducted inaccordance with Test Method SAE J912, entitled “Test Method forDetermining Blocking Resistance and Associated Characteristics ofAutomotive Trim Materials.” The test method is designed to indicate thedegree of surface tackiness, color transfer, loss of embossment, andsurface marring when two materials are placed face-to-face underspecific conditions of time, temperature, and pressure.

Laboratory analysis for blocking entails cutting two 50 mm×75 mmswatches of airbag fabric, pressing a 50 mm×50 mm area under a 5 lb. (22N) load at 100° C. for 48 hours, and allowing a 25 mm×50 mm end flap toremain without exposure to temperature or pressure. At the end of thetesting period, the 22 N-load is removed and a 50-gram mass is attachedto the end flap on the lower fabric swatch. The time required for thetwo coated swatches to peel apart completely is recorded. If the timerequired to separate the fabrics utilizing a 50-gram weight suspendedfrom the bottom fabric layer is greater than 30 seconds, the coatingsystem fails the blocking test.

Clearly, the lower the required separating shear force, the morefavorable the coating. In traditional airbag coating systems (such asthat of Example 2), to improve blocking resistance and thus reduce thechance of improper adhesion between the packed fabric portions,anti-blocking agents (such as talc, silica, silicate clays, and starchpowders) may be applied to the coated fabric. However, the need for suchadditives is eliminated with the present coating compositions, as shownby the results obtained below.

Sample Identification Separation Time Example 1 Immediate Example 2(Comparative) ImmediateThus, the single-layer, urethane-based coating system of Example 1performed as well as the two-layer, talc-applied coating system ofExample 2.

As demonstrated above and as described herein, the present single-layercoating systems described herein provide excellent gas retention,anti-blocking characteristics, flame retardance, and aging stability,making them advancements over previously developed coating systems thatrequire two coating layers to achieve these properties.

1-15. (canceled)
 16. A method of making a coated airbag, said methodcomprising the steps of: (a) providing an airbag; (b) providing acoating composition, said coating composition comprising (i) agas-retaining urethane characterized by a tensile strength at break ofat least 2,500 p.s.i., an elongation at break of at least 300%, and a100% modulus less than 2,000 p.s.i. and (ii) a flame retardant urethanecontaining halogen atoms in the polymer backbone, wherein the dry partsratio of (i) to (ii) is from 50:50 to 80:20; (c) applying said coatingcomposition to at least a portion of said airbag in a single layer; and(d) drying said coating composition.
 17. The method of claim 16, whereinsaid airbag is a one-piece Jacquard woven airbag.
 18. The method ofclaim 16, wherein the application of said coating composition in step(c) is accomplished by a technique selected from the group consisting offloating knife coating, knife-over-roll coating, spray coating,impregnation coating, curtain coating, reverse roll coating, transferroll coating, and screen coating.
 19. The method of claim 16, whereinstep (d) occurs at temperatures between 260° F. and 320° F.
 20. Themethod of claim 16, wherein the dry add-on weight of said monolithiccoating layer is from about 0.5 oz/yd² to about 1.5 oz/yd².